1. Field of the Invention
The present invention relates to a vapor-phase processing method in which a polycrystalline silicon film or a photoresist film is etched or ashed in vapor phase, and an apparatus therefor.
2. Description of the Related Art
The method of etching the polycrystalline silicon layer in vapor phase has been so far employed in constructing MISFET (metal-insulator-semiconductor field effect transistor) using a polycrystalline silicon layer formed on a substrate as a gate electrode, for example, TFT (thin film transistor).
In this vapor-phase etching method, the etching has been so far conducted by exciting a reaction gas with plasma discharge and applying the same to a substrate or a film on the substrate for reaction to vaporize the reaction product for etching. In this reactive etching using plasma, a plasma potential (cathode drop) usually occurs owing to a difference in mobility in a group of electrons or ions to allow acceleration by the potential gradient. Since the electric field by this potential is vertical to a substrate, ions or radicals are vertically applied to the substrate whereby the etching selectivity is obtained.
However, the use of plasma in this etching involves the following defects.
(1) A non-uniform electric field is generated on the substrate owing to a non-uniform plasma electric field, fluctuation and plasma induction charge, thereby causing damage and short-circuiting of a transistor (increase in charge of a gate oxide film, discharge breakdown and discharge between wires). This phenomenon tends to occur in on/off action of plasma in particular.
(2) There is a possibility of ultraviolet damage due to light emission from plasma.
(3) Metals on an inner wall of a device are damaged with plasma to cause cross contamination of metallic atoms.
(4) Plasma discharge in a large area is difficult, and a standing wave is generated, so that uniformity is hardly obtained.
(5) A device is complicated and costly, and maintenance thereof is troublesome.
Such problems due to plasma also occur when a photoresist is ashed by plasma discharge.
Under these circumstances, the invention aims to provide a method in which etching (further ashing) is conducted by imparting satisfactory kinetic energy to reaction seeds such as ions or radicals and further controlling kinetic energy without damaging a substrate, and an apparatus used in this method.
That is, the invention relates to a vapor-phase processing method, which comprises etching or ashing a substrate or a film on the substrate with reaction seeds or precursors thereof generated by contacting a reaction gas with a catalyst heated. Further, it is possible that an electric field of less than a glow discharge starting voltage acts on reaction seeds or precursors thereof generated to give directional kinetic energy.
Still further, the invention is to provide a vapor-phase processing apparatus comprising a reaction gas feeding unit, a catalyst, a heating unit of the catalyst and a suscepter for supporting a substrate or a substrate with a film to be etched or ashed. The vapor-phase processing apparatus can further comprises an electric field applying unit for applying an electric field of less than a glow discharge starting voltage.
According to the method and the apparatus therefor in the invention, since the reaction seeds or the precursors thereof generated by contacting the reaction gas with the catalyst heated are used in the etching or the ashing, the following marked functional effects can be obtained.
(1) The reaction seeds or the precursors thereof are led to the substrate at good efficiency by imparting satisfactory kinetic energy owing to the catalytic activity of the catalyst and its heat energy, and the etching or the ashing proceeds by the chemical reaction and the collision against the substrate. Therefore, the pattern etching or ashing can be conducted with low damage without ultraviolet damage. Consequently, upon covering the defects of the ordinary reactive etching, for example, selective etching of polycrystalline Si, selective etching of SiO2, on Si, etching of an Al alloy by a sputtering effect, removal of Al2O3 on Al, etching of copper or high-melting metals and removal of a resist degenerated layer after implantation of ions at high dose can easily be conducted satisfactorily.
(2) An etching selection ratio can freely be determined depending on a heating temperature of a catalyst, a type of a catalyst, and a type and conditions of a reaction gas. Thus, various fine processings such as anisotropic etching, isotropic etching, controlling of an angle of inclination on an edge and surface flattening by setting a selection ratio at 1 are enabled.
(3) Since the directional acceleration voltage by the electric field is imparted to the reaction seeds or the precursors thereof in addition to the catalytic activity of the catalyst and its heat energy, kinetic energy is increased to lead the same to the substrate at good efficiency, whereby the etching or the ashing proceeds by the chemical reaction and the collision against the substrate. Accordingly, since the etching is the anisotropic etching like the reactive ion etching, the high-precision pattern etching or ashing can be conducted with low damage without ultraviolet damage. As a result, the high-anisotropic etching is enabled through impact of ions entered vertically upon covering the defects of the ordinary reactive etching. Consequently, for example, selective etching of polycrystalline Si, selective etching of SiO2 on Si, etching of an Al alloy by a sputtering effect, removal of Al2O3 on Al, etching of copper or high-melting metals and removal of a resist degenerated layer after implantation of ions at high dose can easily be conducted satisfactorily.
(4) An etching selection ratio can freely be determined depending on a type of an acceleration voltage [direct current (DC) voltage, low-frequency voltage superposed on direct current voltage (AC/DC) or radiofrequency voltage superposed on direct current voltage (RF/DC)], its value, a heating temperature of a catalyst, a type of a catalyst, and a type and conditions of a reaction gas. Thus, various fine processings such as anisotropic etching, isotropic etching, controlling of an angle of inclination on an edge and surface flattening by setting a selection ratio at 1 are enabled.
(5) Since plasma is not generated, damage or short-circuiting, ultraviolet damage and cross contamination of metals by plasma do not occur.
(6) Since reaction seeds (ions or radicals) generated with a catalyst are led to a substrate at good efficiency, a reaction gas is used at high efficiency, and a treatment rate is increased, thereby improving a productivity and reducing costs by reduction of a reaction gas.
(7) In comparison with reactive etching with plasma, quite a simple, inexpensive apparatus is realized. In this case, operation is conducted under reduced pressure or under normal pressure. In the reduced pressure operation, a simpler, less costly apparatus can be realized than in the normal pressure operation.
(8) Since kinetic energy of reaction seeds is great, treatment in a large area is enabled. Even when a substrate temperature is decreased, the treatment can be conducted, and a large-sized, less costly insulation substrate (glass substrate or heat-resistant resin substrate) is also available. In this respect, costs can also be reduced.